The present invention relates to a method and an apparatus for applying a belt-shaped bead filler on a bead core with apex, in which the bead filler cords, at the overlapping joint portion thereof, are prevented from being disturbed in the arrangement angles so as not to cause staggered joint and wrinkle.
As schematically shown in FIG. 15, at the tire bead equipped with an annular bead core A, an apex B extending outward in the radial direction is provided and also a bead filler C forming a reinforcing layer by folding up from an internal circumferential surface AQ of the bead core A toward both side faces of the apex B is provided inside of at least one layer of a carcass P.
For such a bead filler C, as shown roughly in FIG. 16, generally used is a belt-shaped sheet body having filler cords D composed of organic fibers such as nylon, or inorganic fibers such as steel arranged parallel with a specified inclination (for example, 45 degrees) to the longitudinal direction and covered with raw rubber.
Meanwhile, certain apparatuses for applying such a bead filler C around on the bead core A were proposed, for example, in Japanese Patent Publication No. 52-36783 and Japanese Laid-Open No. 59-209844. In such conventional apparatuses, however, a starting edge CT of the bead filler C is attached to the internal circumferential surface AQ of the bead core A and then the bead filler is folded up around the bead core A outward in the radial direction gradually from the starting edge CT according to the rotation of the bead core A.
But in such a construction the bead filler C was gradually folded up along the bead core A at the same time the bead filler C was being fed to the internal circumferential surface AQ of the bead core A, and since the starting edge CT which was the starting portion for folding up the bead filler C and the terminating edge CE which was the end portion of folding were so-called free ends which tended to deform easily, deformation in folding-up was caused, especially at a knife tip portion ET which became a sharp triangular shape generated at an edge because of a slant cutting along a filler cord D (shown in FIG. 16), to fold up the filler cord D, as shown by a solid line in a circled part in FIG. 17, at a larger angle in the radial direction than the original cord angle (for example, 45 degrees). While at an obtuse triangular portion EE on the other edge, the change of cord angles was scarcely generated as shown by broken lines in FIG. 17.
As a result, at the joint overlapping portion J where the knife tip portion ET of the starting edge CT was superposed on the obtuse triangular portion EE of the terminating edge CE, owing to the standing-up of the cord at the knife tip portion ET, mismatching of cord angles occured and the filler cords D crossed each other so as to generate a so-called staggered joint (an offset at the joint, shown in the circle in FIG. 17). Accordingly, a tire with a uniform internal structure cannot be produced because of formation of wrinkles at the portion and adverse effects were exerted on the quality of the tire such as filler cord looseness and deterioration of force variation. The joint stagger moreover became more apparent according to the folding height, that is, the length from the internal circumferential surface AQ to the upper edge AP of the folded part increased.